Electro-pneumatic transducer

ABSTRACT

A lever beam is mounted for pivotal movement, with electromagnetic forces applied to one end, and pneumatic forces applied to the other. A nozzle applies pressurized air against a planar surface of a baffle plate and provides a pneumatic signal that is a function of the distance between the nozzle opening and the planar surface. An alignment mechanism adjusts the planar surface parallel to the nozzle opening to provide a close fit cut-off. A span adjustment controls the position of the nozzle. A damper is coupled to the lever beam at the fulcrum and assumes the pivot point of the lever mechanism. An zero mechanism is provided for balancing the lever under a zero signal input condition.

United States Patent Mitchell et al.

ELECTRO-PNEUMATIC TRANSDUCER Inventors: Wayne D. Mitchell; Paul T. Metzger, both of Rochester, NY.

Assignee: Sybron Corporation, Rochester,

Filed: Jan. 11, 1974 Appl. No.: 432,511

US. Cl 137/82, 74/89.l5, 251/80 Int. Cl GOSd 16/00, F16b 5/00 Field of Search 137/82, 85, 86; 251/80,

References Cited UNITED STATES PATENTS 1l/l96l 3/1963 5/1965 5/1967 8/1967 Borthwickni: 137/85 Primary Examiner-Alan Cohan Attorney, Agent, or Firm-Theodore B. Roessel; J. Stephen Yeo; Charles C. Krawczyk [57] ABSTRACT A lever beam is mounted for pivotal movement, with electromagnetic forces applied to one end, and pneumatic forces applied to the other. A nozzle applies pressurized air against a planar surface of a baffle plate and provides a pneumatic signal that is a func' tion of the distance between the nozzle opening and the planar surface. An alignment mechanism adjusts the planar surface parallel to the nozzle opening to provide a close fit cut-off. A span adjustment controls the position of the nozzle. A damper is coupled to the lever beam at the fulcrum and assumes the pivot point of the lever mechanism. An zero mechanism is provided for balancing the lever under a zero signal input condition.

14 Claims, 13 Drawing Figures N MI! PATENIED JANZI I975 SHEET 2 OF 5 om mm 00 4% on Q wow mm .NN

PATENTED JANE] I975 SHEET 4 OF 5 ELECTRO-PNEUMATIC TRANSDUCER BACKGROUND OF THE INVENTION This invention pertains to transducers in general, and more particularly to electro-pneumatic transducers wherein a feedback is provided for balancing the transducer.

Electro-pnuematic transducers are used in many control systems wherein it is desired to convert electrical signals into pneumatic signals, or to convert pneumatic signals into electrical signals. Such transducers generally include a lever mechanism wherein electromagnetic forces are applied to one end of the lever mechanism while the pneumatic forces are applied, or detected, from the other end of the lever mechanism under an arrangement wherein the electromagnetic and pneumatic forces are balanced to provide a steady state output condition. The pneumatic forces are applied to the lever mechanism by a nozzle type of assembly or by a bellows mechanism. Electromagnetic forces are usually applied by a coil positioned in a magnetic assembly. The spacing between the nozzle assembly and the lever mechanism is inversely proportional to the electromagnetic force applied to the lever mechanism. The back pressure produced by the nozzle assem bly (which is a function of the distance between the nozzle assembly and the lever mechanism) is used to provide an output signal that is a function of the magnitude of the input electromagnetic force applied to the other end of the lever mechanism. Alternately, a bellows type of pneumatic device can be connected to the lever mechanism instead of the nozzle assembly wherein a pressure in the bellows is the input signal and is balanced by an electromagnetic feedback force, which would represent the output signal. In order to get a maximum signal output from a nozzle feedback arrangement, it is necessary that when a force of sufficient strength is applied by the electromotive means to bring the lever toward the nozzle assembly to a closed" condition, the fit or alignment between the two elements is such as to provide a maximum back pressure.

Nozzle arrangements using a ball valve are disclosed in a U.S. Pat. No. 2,669,247, issued on Feb. 16, 1954 to G. Olah entitled Fluid-Pressure Operated Device and a U.S. Pat. 3,004,546 issued on Oct. 17, 1961 to J. W. Robins et al. entitled Electro-pneumatic Transducer. Although the ball valve arrangement provides a good alignment through the use of a spherical shape of a ball, such type of valve is particularly susceptible to dirt, wherein any dirt that may collect on the surface of the ball from the air being throttled will create a poor fit and a leakage condition, which results in a drift in the back pressure, and a loss of instrument accuracy thereby requiring a periodic cleaning thereof.

Other systems of the prior art have used a needle valve type arrangement such as that disclosed in a U.S. Pat. No. 3,164,333 issued on Jan. 5, 1965 to J. D. Robertson entitled Tension Controlled System for a Web- Feeding Mechanism and a U.S. Pat. No. 3,240,058 issued on Mar. 15, 1966, to R. H. Foster entitled Continuous Tension Monitor for Web'Feeding Mechanisms." The needle valve arrangement includes a conical shaped valve seat into which a cone shaped valve stem extends. in order to get a close fit, the valve seating and valve stem must be accurately machined. In addition to the foregoing, when mounted in the assembly, care must be taken to accurately assure that the valve seat and the valve stem are perfectly aligned to provide the desired maximum back pressure.

Another type of nozzle arrangement includes a nozzle baffle plate combination wherein a cone shaped nozzle arrangement is provided with an opening in the center thereof while a flat planar shaped baffle is positioned adjacent the nozzle opening to control the back pressure thereto or control the flow of air therefrom. Such combined nozzle-baffle plate assemblies are illustrated in a U.S. Pat. No. 2,837,107 issued on June 3, 1958 to F. W. Slide entitled Rotary to Linear Motion Transducer, a U.S. Pat. No. 3,173,473 issued on Mar. 16, 1956, to R. B. Adams, entitled Transducers, and a U.S. Pat. No. 3,183,918 issued on May 18, 1965 to A. Bester entitled Transducer Assembly for Transformation of Small Forces into Pneumatic Pressures." With such nozzle-baffle type of assembly, in order to obtain a maximum back pressure signal, it is very important that when the baffle plate is moved adjacent to or engages the nozzle assembly, the planar surface of the baffle is parallel with the opening in the nozzle so as to provide a close alignment to allow a minimum amount of air flow. With the prior art arrangements the baffle assemblies lack adjustments for a simple and accurate means for assuring the desired degree of alignment. Often the lever beam is bent to attempt to obtain the parallel relation. Such an adjustment is difficult and time consuming. Even if the lever mechanism can be bent to provide the close fit, if a span adjustment is provided of the type illustrated in the Bester patent, any change in the span adjustment changes the positioning of the nozzle opening relative to the baffle plate and requires a subsequent bending and adjusting of the lever mechanism to provide the necessary parallelism.

The span adjustment can accomplished by adjusting the magnetic sensitivity of the electromagnetic transducer rather than the nozzle, such as illustrated in the Robins et al. patent, or as illustrated in a U.S. Pat. No. 3,009,084 issued on Nov. 14, 1961 to C. G. Balliett, entitled Electromechanical Transducer." Although this type of arrangement proved to be satisfactory, it is generally desired to maximize the sensitivity of the electromagnetic device and adjustments of this type tendto be costly in order to achieve the required stability of adjustment.

A ball and socket type of arrangement was provided in the prior art for the nozzle-baffle plate arrangement wherein the baffle plate was mounted in a ball swivel type fitting so that the planar surface of the plate could be rotated to a position to provide the proper alignment, and then secured in that position by a locking device. Such an arrangement proved to be satisfactory however, required a time consuming adjustment since great care must be taken when locking the baffle assembly in position so that the locking device does not shift the selected setting. Very often, several attempts in adjusting the baffle plate were required. 1t would therefore be highly desirable, if some sort of simple adjustment mechanism can be provided for adjusting the alignment between a nozzle and a baffle plate that provides the required degree of parallelism (close fit) without requiring a series of adjustments and wherein the nozzle can be used as a span adjustment without requiring a subsequent adjustment of the baffle plate.

The electro-pneumatic transducers of the prior art generally include a zero adjustment for balancing the transducer for a zero signal condition. Such a balance adjustment is generally provided by a screw type adjustment that sets the tension on a spring to provide balancing force, such as that illustrated in the Robins et al. and Bester patents. Such an adjustment is quite critical, and once set, is required to be locked into place. With the zero adjustments of the prior art, frietion, backlash, etc., of the adjusting device was a problem in attempting to obtain a desired zero balance setting. As a result, various rocking type adjustments were required to be made to attempt to achieve the zero type adjustment. And once the zero type adjustment was achieved, the screw adjustment was required to be secured by a locking device. Often the setting of locking device changed the bias setting requiring another adjustment. It would therefore be highly desirable if some sort of zero adjustment arrangement could be provided for electro-pneumatic transducers wherein backlash can be essentially eliminated and the need for locking device avoided.

At times, it is highly desirable to provide some sort of damping mechanism for electro-pneumatic transducers so that the response of the transducers to spurious noise, etc., can be reduced. Such a damper should be secured to the lever mechanism without detrimentally effecting the transducer operation. The damper should be such that it does not affect the balance or pivot point of the lever, does not affect the span adjustment, does not effect the baffle plate setting, and does not affect the low frequency sensitivity or accuracy of the transducer.

Control instruments including eleetro-pneumatic transducers are often located in a variety of locations, such as for example on pipes, valves, etc. The oriention of the control instrument may vary depending upon the particular location in which the instrument is to be mounted. Hence, it would be highly advantageous if electro-pneumatic transducers functioned in any physical orientation providing flexibility in mounting. In addition to the foregoing, once the instrument is mounted and calibrated, a change in the control system may re quire a subsequent relocation, or in the event of an accident the instrument or its mounting may be moved. Hence it would be highly advantageous if electropneumatic transducers could be subject to reorientation without materially affecting the force balance operation of the transducer to the extend of requiring a recalibration.

It is therefore an object of this invention to provide a new and improved electro-pneumatic transducer.

It is also an object of this invention to provide a new and improved electro-pneumatic transducer including means for readily adjusting the alignment (parallelism) of a nozzle-baffle plate assembly.

It is a further object of this invention to provide a new and improved electro-pneumatic transducer wherein once the parallel relation between the nozzle-baffle plate assembly is made, the nozzle can be moved to set the span adjustment without materially effecting the alignment.

It is also an object of this invention to provide a new and improved electro-pneumatic transducer including an anti-backlash zero adjustment that does not need a locking device to hold the setting.

It is a further object of this invention, to provide a new and improved electro-pneumatic transducer including a damper mechanism.

It is also an object of the invention to provide a new and improved electro-pneumatic transducer that is orientation insensitive and can therefore be mounted in any position.

It is still a further object of this invention to provide a new and improved electro-pneumatic transducer, that once calibrated, can be subsequently positioned in any orientation without materially affecting its calibration.

BRIEF DESCRIPTION OF THE INVENTION A transducer comprising lever means including a lever beam mounted for pivotal movement and including a baffle plate extending from one end of the lever beam. Electromagnetic means are coupled to the other end of the beam. Pneumatic means, including a nozzle assembly, is positioned to apply pressurized air against a planar surface of the baffle plate. The pneumatic means provides an output signal that is a function of the distance between the nozzle opening and the planar surface. Alignment means are provided for adjusting the position of the planar surface of the baffle plate relative to the nozzle opening so that when the baffle and nozzle are brought together, the planes of the baffle and the nozzle opening are parallel to minimize the flow of air from the nozzle opening.

In accordance with the features of the invention, the planar surface of the baffle extends towards the fulcrum of the lever mechanism wherein the nozzle means can be moved as a span adjustment without materially effecting the alignment of the baffle plate.

In accordance with another feature of the invention, a pivotal damping means is coupled to the lever at the fulcrum. The damping means includes flexible potion that functions as a pivot point for the damping means wherein the pivot point automatically corresponds to the fulcrum when coupled to the lever beam. The mass of a movable element in the damping means and its center of gravity can be selected to provide a static balance for the lever mechanism making the electropneumatic transducer orientation insensitive.

A still further feature of the invention includes an zero adjustment means, having essentially no backlash and/or deadband, coupled to the lever beam for applying an adjustable resilient force to the lever means to provide a zero signal balance condition.

BRIEF DESCRIPTION OF THE FIGURES FIG. I is a top view of a electro-pneumatic transducer including the invention.

FIG. 2, is a side view of the electro-pneumatic transducer of FIG. 1 taken along lines 22.

FIG. 3 is a bottom view of the electro-pneumatic transducer of FIG. 1.

FIG. 4 is a bottom view of the lever beam mechanism of the transducer of FIG. 1.

FIG. 5 is a side view of the lever beam mechanims of FIG. 4.

FIG. 6 is a top view of the span adjustment for the eleetro-pneumatic transducer of FIG. 1.

FIG. 7 is a sectional view of the span adjustment of FIG. 6 taken along lines 7-7 to illustrate the operation of the span adjustment.

FIG. 8 is a partial side view of the electro-pneumatic transducer to illustrate an zero adjustment.

FIG. 9 is a top view of the carriage of the zero adjustment of FIG. 8.

FIG. 10 is a front view of the carriage of FIG. 9.

FIG. 1 1 is a sectional view of a damper of the electropneumatic transducer of FIG. 1.

FIG. 12 is a top view of the damper of FIG. 11.

FIG. 13 includes a bellows type pressure transducer replacing the nozzle-baffle plate assembly of FIGS. 1-7.

DETAILED DESCRIPTION OF THE INVENTION The electro-pneumatic transducer includes a lever beam 12 mounted for pivotal movement about a pivot axis designated by the dashed lines 14. One end of lever 12 is coupled to an electromagnetic transducer 16, while the other end is coupled to a nozzle-baffle plate arrangement including a nozzle assembly 18 and a baffle plate 20. A pivotal damper 22 is secured to the lever beam 12 and includes its pivot at the pivot axis 14. A zero bias adjustment 24 is connected to the lever beam 12 to set the mechanism to a balanced position for zero signal input condition. The electromagnetic transducer 16 is a standard type including a cup shaped magnetic structure 26 of the type generally used in speakers. A pair of wires 28 are connected via a pair of terminals 30 to a coil 32 positioned within the air gap of the magnetic assembly 26. In response to a DC current flow through the coil 32, a force is generated by the magnetic flux in the air gap to pivot the lever beam 12 in the direction of the arrow 34 (FIG. 2). This type of electromagnetic transducer is well-known in the art and does not require any further explanation.

The nozzle assembly 18 includes an input port 40 for receiving pressurized air and an output port 42 for providing a signal that is the back pressure created by the baffle plate on the air flow from nozzle outlet 44 (a function of separation between the baffle plate planar surface 46 and the nozzle or outlet 44). The nozzle 44 has the shape of an annular ring (FIG. 6) and lies in a plane generally parallel to the base 48 of the transducer. The diameter of the nozzle 44 is such so that the force created over its area, for the normal output pressure, balances the input electromotive force exerted on the lever. The nozzle back pressure is applied to the baffle plate 20 creating a force in the direction of the arrow 47.

The baffle plate 20 is secured to the end of the lever beam 12 by a bolt 50 passing through spacer 51 and by two adjustment screws 52 and 54. The adjustment screws 52, and 54 provide a means for adjusting the setting of the planar surface 46 of the baffle plate 20 relative to the plane of the outlet 44 of the nozzle assembly as will be explained in greater detail in later portion of the specification.

The lever beam 12 is mounted to the transducer base 48 by a C shaped bracket 56, the screws 59 and a two pairs of leaf spring assemblies 60 and 62 (FIGS. 4 and 5). A pair of projections 64 and 66 extend from the lever beam 12. The projections include an leg 68 secured to the lever beam 12 and a foot 70 extending normal thereto. The bracket 56 have generally S-shaped ends with the portions 72 and 74 being parallel to the foot 70. In addition, the bracket 56 includes a pair of tabs 76 that extend therefrom into the base 48 to serve as an alignment means for mounting the damper 22, as

will be discussed in greater detail in a later portion of the specification. The spring assemblies and 62 are formed of two leaf springs 78 and 80 (FIG. 5) disposed generally normal to each other. The foot of each .projection 64 and 66 is secured to the end portion 72 of the bracket 56 via the leaf spring 78. The leg 68 of each extension 64 and 66 is secured to the corresponding tab 76 of the bracket 56 via the leaf spring 80. The point at which the leaf springs 78 and cross define the pivot axis 14 of the lever beam 12. The pivot axis 14 extends through the cross-over points of the leaf spring 78 and 80 of both the spring assemblies 60 and 62.

As can be seen, the lever beam 12 pivots about the axis 14 in response to a force generated by the electromagnetic transducer 16 in a direction of the arrow 34 until balanced by a pneumatic force from the nozzle as sembly 18 on the baffle plate 20 in the direction of the arrow 47. If the force from the electromagnetic transducer 16 is of sufficient magnitude, the lever beam 12 pivots until the planar surface 46 of the baffle plate 20 engages the nozzle 44. At this time, a maximum back pressure is be generated in the nozzle assembly 18 to produce a maximum pneumatic output signal at the port 42. The magnitude of the output pneumatic signal depends, to a large degree, by the amount of leakage between the baffle plate 20 and the nozzle assembly 18. In order to achieve maximum backpressure when the baffle plate abuts against the nozzle assembly, the planar surface 46 of the baffle plate 20 must be parallel to the plane of the annular shape nozzle or outlet 44. This provides a close fit or parallelism to minimize pneumatic leakage therebetween. This parallel relation is set by first securing the bolt 50 so that the separation between the planar surface 46 of the baffle plate 20 and the lever beam 12, as preset by the spacer 51, corresponds to the distance between the pivot axis 14 and the lever beam 12. The distance from the nozzle 44 and the base 48 also is approximately equal to the distance between the axis of rotation 14 and the base 48. These dimensions are selected so that, when the baffle plate 20 is so positioned, the planar surface 46 extends through the pivotal axis as illustrated by the dashed line of FIG. 5. This arrangement, allows the movement of the nozzle assembly 18 to function as the span adjustment without materially upsetting the parallel relation between the planar surface 46 and the nozzle 44, thereby generally requiring no further adjustment of the baffle plate 20.

Once the bolt 50 is secured, the lever beam 12 is depressed so that the the surface 46 contacts the nozzle 44 and the screws 52 and 54 are adjusted for a maximum output from the port 42. When this maximum output is achieved, the planar surface 46 is parallel to the plane of the nozzle 44. No further adjustments of the baffle plate are required. There is no need for any locking devices to lock the baffle 20 in place. A tight thread arrangement is provided for the bolt 50 and the screws 52 and 54 and the baffle plate 20 to provide friction to keep the adjustment in place. In addition, three springs 92, are located between the lever beam 12 and the baffle plate 20 that individually surround the bolt 50 and the screws 52 and 54 to provide a resilient force therebetween to further assure that the adjustment will be maintained.

According to a feature of the invention, the nozzle assembly 18 (FIG. 6) extends through an elongated aperature 94 formed in the base 48 that lies in the general direction of the lever beam 12 and is secured via the screws 97 (FIGS. 2 and 3) to a carriage 96 positioned on the transducer base 48. The carriage 96 is held in place by a pair of offset cam adjustments 100 and 102. Each of the offset cam adjustments 100 and 102 includes a cylindrical shaft 104 (FIG. 7) that extends through a base aperature 106 an eccentric cam 114 a larger clamp 110 and includes a slotted top 108 to allow a screwdriver adjustment thereof. The clamp 110 is located between the carriage 96 and the slotted top 108 and has a diameter greater than the width the U- shaped openings 112 formed in the opposite ends of the carriage 96. The cams 100 and 102 are located within the U-shaped aperatures 112 and are offset relative to the aperature 106. The arrangement is such that the span adjustment of the transducer can be adjusted in accordance with the invention by setting either one of the offset cam adjustments 100 and 102, or both. As can be see, as the offset adjustment is rotated, the offset cam 114 engages the U-shaped aperature 112 within the carriage 96 to, depending upon the direction of rotation of the shaft 104, move the nozzle assembly 18 along the direction of the elongated aperature 94. As in the case of the baffle plate adjustment, there is no lock type devices needed for the span adjustment. The force of the clamp device 116 and the friction between the base 48, the carriage 96, and the cams 100 and 102 is sufficient to maintain the span adjustment in its preset position.

In accordance with a further feature of the invention, the damper 22 is connected to the lever beam 12 to provide a damping function. As illustrated in FIGS. 11 and 12, the damper includes a paddle 130 that is immersed in a silicone liquid 132 and is secured at the end 134 to the damper housing 136 via a collar 138 made of a resilient material, such as for example rubber. The paddle 130 is secured to the lever beam 12 by the screw 140 which extends into a threaded aperature 142 in the free end of the paddle 130. The damper 22 is secured to the transducer base 48 by a pair of screws 144 which extend through the aperatures 146 in the damper 22. The entire damper is filled with a silicone liquid leaving no air or voids. As a result, the paddle 130 is continuously immersed in the liquid and therefore the damping effect is insensitive to its orientation. The resilient collar or seal 138 forms a compression type seal with the paddle 130 to provide a slip type fitting that allows the rotational movement of the paddle 130 (relative to the seal 138) for aligning the paddle top relative to the aperature 131 in the lever beam 12. A pair of slots 148 are formed in the damper base to align with the tabs 76 of the bracket 58. Since the damper 52 has the flexible collar 138, the damper 22 automatically selects a pivot point that corresponds to the pivot axis 14 of the transducer to provide a pivotal damping function for the transducer. The damper 22 has the advantage of merely being able to be secured to the lever 12 and the base 48 to provide the damping function without any further adjustments. The mass of the paddle 130 is selecting and its center of gravity is located relative to the pivot axis 14 so that a static balance is provided for the lever mechanism. This static balance is maintained regardless of orientation. Hence, the electro-pneumatic transducer can be usually repositioned without materially affecting its calibration. The damper is more fully described in a copending U.S. Pat. application Ser. No.

432,520 filed on Jan. 11, I974 for Paul T. Metzger and entitled Damper Mechanism.

In accordance with another feature of the invention. a zero bias mechanism 24 is provided for the transducer that function without any noticeable backlash or deadband. The zero bias adjustment mechanism 24 is coupled to the lever beam 12 via a spring 200. One end of the spring 200 is secured to a collar 202 which in turn is secured to the lever beam 12 by a screw 204. The other end of the spring 200 is secured to a collar 206, which in turn, is secured to an adjustable carriage 208 by a screw 210. The carriage 208 is mounted on the zero adjustment screw 212 by means of a threaded shaft 214 so that as the zero adjustment screw 212 is rotated the carriage 208 moves along the threaded shaft 214.

The shaft 214 includes a threaded section, an elongated bearing section 217 and a slotted end 219. The bearing section is positioned in a cylindrical bearing 221 that is press fitted into the base 48. As illustrated in FIGS. 3, 9, and 10, the carriage 208 is formed with a U-shaped aperature 216 at the end opposite that engaging the threaded shaft 214. A stationary column 218 extends through the U-shaped aperature 216 to function as a guide for the carriage 208 to inhibit its rotational movement. A spring 220 is positioned around the column 218 and urges against the carriage 208 via a moveable collar 222. The downward force created by the spring 220 is applied to the carriage 208 at the carriage sloping surface 228. The radial surface of the collar 222 is such that it establishes a point contact with the sloping surface of the carriage 208. The angle of the sloping surface 228 of the carriage 208 converts the force existing at the contact point into vertical force component and a horizontal force component. The vertical force component creates a rotational moment about the bearing in the direction of the arrow 224, thereby eliminating any backlash between the threads in the carriage 208 and that of the threaded shaft 214. bearing section 217 and the bearing 221. The horizontal force component creates rotational moment about the centerline of the threaded shaft 214 in the direction of the arrow 226, urging the surface 217 of the U- shaped aperature 216 against the column 218. This horizontal rotation tendency of the carriage 208 keeps the surface 217 in contact with the column 218 and thereby eliminates the backlash which would otherwise exist due to the finite clearance required between the U-shaped aperature 216 and guiding column 218.

With the adjustment described, the zero bias for the lever beam 12 can be preset without adjusting or compensating for backlash or deadband when making the setting. In addition to the foregoing, there is no need for any locking devices in the zero bias adjustment since the rotational moment 224 provides a high friction coupling between the threaded shaft 214 and the carriage 208, and the rotational moment 226 provides a strong resilient coupling to the shaft 218 that prevent any change in the setting. The zero bias mechanism 24 is described in greater detail in a copending patent application Ser. No. 432,521 filed on Jan. 11, 1974 for Wayne D. Mitchell and Paul T. Metzger and entitled Adjustment Mechanism.

Although the discussion with regards to FIGS. I-12 has been primarily directed to an electro-pneumatic transducer wherein an electrical input signal is applied via the electro-magnetic transducer 16 and a pneumatic output signal is produced by the nozzle assembly 18, it is to be understood that transducers can be modified according to the invention to produce an arrangement wherein the input signal can be a pneumatic pressure and the output an electrical signal. In such case, the nozzle assembly 18 and the baffle plate are removed and a bellows type transducer 250 substituted therefore as illustrated in FIG. 13. The bellows assembly 250 is secured to the carriage 96 via the screws 25. The pneumatic pressure applied to the bellows assembly 250 via an input port 252 causes a bellows 254 to expand and cause the shaft 255 to move in a direction of the arrow 256. The shaft 254 is secured to the beam 12 by the nut 258 urging against a spring 257 causing the beam to pivot around its axis. This movement changes the electrical signal from a detector coil assembly and by means of an electronic amplifier, generates an output signal which is also applied to the coil 32 within the electro-magnetic transducer 16 creating a feedback balancing force on the lever assembly.

As described above, the electro-pneumatic transducer including the features of the invention, provides for a plurality of adjustments, none of which require any lock type settings. The span adjustment for the transducer is provided by adjusting the position of the nozzle assembly 18 relative to the lever beam 12. There is no need to adjust the sensitivity of the electromagnetic transducer 16. In addition, the baffle adjustment is such that it can be easily preset by the two screws adjustments 52 and 54 to provide an simple and accurate means of assuring a proper alignment (close fit) between the baffle planar surface 46 and the nozzle 44. In addition to the foregoing, the planar surface 46 is in line with the pivot axis of the lever, wherein the span adjustment can be made after the nozzle-baffle adjustment is completed without materially effecting the nozzle-baffle adjustment. Furthermore, a damper 22 is provided for the transducer that is merely secured to the transducer base and the lever beam and that accepts the pivot point of the lever beam, requiring no adjustments. The sealed construction of the damper and the static balance provided by the mass and center of gravity of the damper paddle makes the transducer orientation insensitive. Further, an zero bias adjustment is provided for the transducer that allows the adjustment thereof without the need for compensation for backlash, dead band, etc.

I claim:

1. A transducer comprising:

lever means, including a lever beam, mounted for pivotal movement about a fulcrum, and a planar baffle plate extending from said lever means at one end;

electromagnetic means coupled to said lever beam at the other end;

pneumatic means pneumatically coupled to said lever means, including a nozzle assembly for applying pressurized air through an opening therein against a planar surface of said baffle plate, wherein the open end of said nozzle assembly lies in a plane adjacent to said planar surface, said pneumatic means also includes an output for providing a pneumatic indication that is a function of the back pressure created by the air flow from said nozzle opening against said planar surface, and alignment means, including a plurality of screw devices, for mounting said baffle plate to said lever beam and for adjusting the position of said planar surface of the baffle plate relative to the plane of the nozzle opening so that when said lever beam pivots to cause said planar surface to engage said nozzle opening the planes of said planar surface and said nozzle open end are aligned to provide minimum leakage thcrebetwcen.

2. A transducer as defined in claim 1 wherein:

said plane of said planar surface of said baffle lay in a direction that extends through said lever beam fulcrum, and

said adjustment means includes three screw type devices arranged in a triangular array for controlling the orientation of said planar surface relative to the plane of the nozzle opening.

3. A transducer as defined in claim 2 wherein:

one of said screw devices extends through a spacer between the lever beam and the baffle plate to preset the spacing between the planar surface of the baffle plate and the lever beam to correspond to the spacing between the fulcrum and the lever beam.

4. A transducer as defined in claim 3 including:

resilient means located between said baffle plate and said lever beam for applying a resilient force therebetween.

5. A transducer as defined in claim 1 including:

span adjustment means for moving said nozzle assembly relative to said planar surface in the general direction of said lever beam.

6. A transducer as defined in claim 5 wherein:

a portion of said nozzle assembly extends through an elongated aperature formed in the transducer base which aperature extends along the general direction of said lever beam, and said span adjustment means includes at least one offset adjustable cam for controlling the location of said nozzle assembly within said elongated aperature.

7. A transducer as defined in claim 1 including:

pivotal damping means coupled to said lever means at the fulcrum, said damping means including a flexible portion that functions as a pivot point for said damping means wherein the pivot point of said damping means corresponds to said fulcrum when coupled to said lever beam.

8. A transducer as defined in claim 7 including:

anti-backlash zero adjustment means, coupled to said lever beam, for applying an adjustable resilient force to said lever means.

9. A transducer as defined in claim 7 wherein:

said pivotal damping means includes a housing formed with a cavity filled with a liquid, a post coupled to the lever means and suspended in the liquid by said flexible portion, said flexible portion providing a liquid seal, and wherein the mass and center of gravity of said post extending beyond the pivot point provides a static balance for the lever means.

10. A transducer comprising:

lever means including a lever beam mounted for pivotal movement about a pivot axis;

electromagnetic means coupled to one end of said lever beam;

pneumatic means coupled to the other end of said lever beam;

pivotal damper means coupled to said lever means at said pivot axis, said damping means including a flexible portion that functions as a pivot point for said damping means wherein the pivot point of said damping means corresponds to said pivot axis when coupled to said lever beam; and

a zero bias adjustment including a rotatable threaded 11. A transducer as defined in claim wherein: said pivotal damper includes a post suspended in a liquid by said flexible portion and the mass of the post and the center of gravity relative to the pivot axis is such as to provide a static balance for said lever means.

12. A transducer as defined in claim 11 wherein:

said pneumatic means is a bellows type device, the expansion of which applies a force to said lever beam.

13. A transducer as defined in claim 11 wherein:

said pneumatic means includes a nozzle assembly for applying pressurized air through an opening therein against a planar surface of a baffle plate, and for providing an output that is a function of the spacing between said opening and said planar surface, and including adjustment means for aligning the planar surface relative to said opening.

14. A transducer as defined in claim 13 wherein:

said nozzle opening lies in a plane;

said adjustment means includes the screw type devices arranged in a triangular array for controlling the orientation of said planar surface relative to the 

1. A transducer comprising: lever means, including a lever beam, mounted for pivotal movement about a fulcrum, and a planar baffle plate extending from said lever means at one end; electromagnetic means coupled to said lever beam at the other end; pneumatic means pneumatically coupled to said lever means, including a nozzle assembly for applying pressurized air through an opEning therein against a planar surface of said baffle plate, wherein the open end of said nozzle assembly lies in a plane adjacent to said planar surface, said pneumatic means also includes an output for providing a pneumatic indication that is a function of the back pressure created by the air flow from said nozzle opening against said planar surface, and alignment means, including a plurality of screw devices, for mounting said baffle plate to said lever beam and for adjusting the position of said planar surface of the baffle plate relative to the plane of the nozzle opening so that when said lever beam pivots to cause said planar surface to engage said nozzle opening the planes of said planar surface and said nozzle open end are aligned to provide minimum leakage therebetween.
 2. A transducer as defined in claim 1 wherein: said plane of said planar surface of said baffle lay in a direction that extends through said lever beam fulcrum, and said adjustment means includes three screw type devices arranged in a triangular array for controlling the orientation of said planar surface relative to the plane of the nozzle opening.
 3. A transducer as defined in claim 2 wherein: one of said screw devices extends through a spacer between the lever beam and the baffle plate to preset the spacing between the planar surface of the baffle plate and the lever beam to correspond to the spacing between the fulcrum and the lever beam.
 4. A transducer as defined in claim 3 including: resilient means located between said baffle plate and said lever beam for applying a resilient force therebetween.
 5. A transducer as defined in claim 1 including: span adjustment means for moving said nozzle assembly relative to said planar surface in the general direction of said lever beam.
 6. A transducer as defined in claim 5 wherein: a portion of said nozzle assembly extends through an elongated aperature formed in the transducer base which aperature extends along the general direction of said lever beam, and said span adjustment means includes at least one offset adjustable cam for controlling the location of said nozzle assembly within said elongated aperature.
 7. A transducer as defined in claim 1 including: pivotal damping means coupled to said lever means at the fulcrum, said damping means including a flexible portion that functions as a pivot point for said damping means wherein the pivot point of said damping means corresponds to said fulcrum when coupled to said lever beam.
 8. A transducer as defined in claim 7 including: anti-backlash zero adjustment means, coupled to said lever beam, for applying an adjustable resilient force to said lever means.
 9. A transducer as defined in claim 7 wherein: said pivotal damping means includes a housing formed with a cavity filled with a liquid, a post coupled to the lever means and suspended in the liquid by said flexible portion, said flexible portion providing a liquid seal, and wherein the mass and center of gravity of said post extending beyond the pivot point provides a static balance for the lever means.
 10. A transducer comprising: lever means including a lever beam mounted for pivotal movement about a pivot axis; electromagnetic means coupled to one end of said lever beam; pneumatic means coupled to the other end of said lever beam; pivotal damper means coupled to said lever means at said pivot axis, said damping means including a flexible portion that functions as a pivot point for said damping means wherein the pivot point of said damping means corresponds to said pivot axis when coupled to said lever beam; and a zero bias adjustment including a rotatable threaded member, a carriage mounted on the threaded member via a threaded coupling for movement in response to the rotation of the threaded member, first resilient means coupling the carriage to the lever beam, guide means for preventing the rotation of said carriage, and second resilient means continUously urging against said carriage to apply a first rotational movement to said threaded coupling to provide a tight coupling therebetween and a second rotational moment continuously urging the carriage against the guide means to provide a tight coupling therebetween.
 11. A transducer as defined in claim 10 wherein: said pivotal damper includes a post suspended in a liquid by said flexible portion and the mass of the post and the center of gravity relative to the pivot axis is such as to provide a static balance for said lever means.
 12. A transducer as defined in claim 11 wherein: said pneumatic means is a bellows type device, the expansion of which applies a force to said lever beam.
 13. A transducer as defined in claim 11 wherein: said pneumatic means includes a nozzle assembly for applying pressurized air through an opening therein against a planar surface of a baffle plate, and for providing an output that is a function of the spacing between said opening and said planar surface, and including adjustment means for aligning the planar surface relative to said opening.
 14. A transducer as defined in claim 13 wherein: said nozzle opening lies in a plane; said adjustment means includes the screw type devices arranged in a triangular array for controlling the orientation of said planar surface relative to the plane of the nozzle opening. 